Effects of CaF2-CuO additives and various firing temperatures on characteristics of alite calcium sulfoaluminate clinkers

Different compositions of alite calcium sulfoaluminate (ACSA) clinkers were synthesised for use as an alternative, more environmentally friendly binder than ordinary Portland cement (OPC). ACSA clinkers have a lower firing temperature than OPC clinkers, thus reducing carbon dioxide emissions during processing. Calcium fluoride (CaF2) and copper oxide (CuO) were added to the raw materials and the resulting phase formation for clinkers was compared with and without these additives. Three different compositions of ACSA clinkers as well as six different firing temperatures were tested and evaluated. Results revealed that the additives accelerated initial formation of C3S at as low as 1100 °C. The ability to process ACSA at such a low temperature enabled the coexistence of C3S - C4A3 S¯ phases in the clinker, while SO3 content greatly influenced C3S crystal formation. Unexpected CaSO4⋅2H2O loss due to evaporation in the firing process initially reduced the C4A3 S¯ phase content below the designed target. Using additional CaSO4⋅2H2O subsequently increased C4A3 S¯ content to the target level when the experiment was repeated using the optimal composition and temperature.